The present invention relates to a process of producing cycloolefin in which monocyclic aromatic hydrocarbon is partially hydrogenated, and more particularly to a process of producing cyclohexene comprising subjecting benzene to a partial hydrogenation reaction. The cycloolefin produced according to the present invention is useful as a raw material for lactams, dicarboxylic acid and the like which are raw materials of polyamides, or as an intermediate raw material for lysine, medicines, agricultural chemicals or the like.
It is known in the art that cycloolefin is produced by various methods such as a partial hydrogenation of monocyclic aromatic hydrocarbon, dehydration of cyclo-alkanol, dehydrogenation or oxidation-dehydrogenation of cycloalkane, or the like. Among them, if cycloolefin could be produced at high efficiency by a partial hydrogenation of a monocyclic aromatic hydrocarbon, such a method is preferred because it is a simplified reaction processes.
In the prior method in which cycloolefin is produced by partial hydrogenation of monocyclic aromatic hydrocarbon, the partial hydrogenation reaction is generally conducted in the presence of water using a catalyst composed primarily of metallic ruthenium. Many such catalysts have been proposed. For example, Japanese Patent Application Laid-open (KOKAI) Nos. 61-50,930(1986), 62-45,541(1987) and 62-45,544(1987) and U.S. Pat. No. 4,734,536 disclose methods in which the metallic ruthenium itself is used in the form of fine particles as the ruthenium-containing catalyst. Further, Japanese Patent Application Laid-open (KOKAI) Nos. 57-130,926(1982) and 61-40,226(1986) and U.S. Pat. No. 5,157,179 disclose methods in which ruthenium used is supported on a carrier such as silica, alumina, barium sulfate, zirconium silicate or the like.
It is also known in the art to use ruthenium in combination with gold, silver, copper, iron, cobalt, manganese or the like to enhance a selectivity of the cycloolefin, as disclosed in Japanese Patent Application Laid-open (KOKAI) No. 53-63,350(1978), U.S. Pat. Nos. 5,157,179 and 4,575,572. Particularly, U.S. Pat. No. 4,575,572 discloses a method in which barium sulfate is used as a carrier and three catalytically active metal components, i.e., ruthenium, either iron or cobalt, and either copper or silver are supported in combination on the carrier to obtain a ternary catalyst system.
Many of the prior procedures require the use of an additive such as a metal salt, an acid or an alkali added to the reaction system. The reason why the addition of the additive is needed, is that the reaction system without an additive disadvantageous from an industrial standpoint due to its extremely low selectivity towards the desired cycloolefin, though the reaction rate generally increases in such a reaction system using no additive.
However, when the additive such as a metal salt, etc. is added to the reaction system, the reaction system exhibits a strong corrosion property so that the attrition or deterioration of the reaction apparatus and catalyst are undesirably accelerated (Dyes and Medicines, vol. 31, No. 11, pp. 297 to 308, 1986). Because of this, further proposals have been made. For example, Japanese Patent Application Laid-open (KOKAI) No. 62-67,033(1987) discloses a method in which a nickel-coating layer is formed on a portion of a reaction vessel which comes into contact with a liquid. Japanese Patent Application Laid-open (KOKAI) No. 62-81,331(1987) discloses a method in which a reaction vessel made of titanium or zirconium is used. In addition, Japanese Patent Application Laid-open (KOKAI) No. 6-128,177(1994) discloses a method in which the reaction vessel made of a nickel-based alloy containing chromium and/or molybdenum is used. In these methods, the above-mentioned problem is overcome by using a generally expensive material for the reaction vessel. However, such a reaction vessel might also suffer from deficiencies such as corrosion or hydrogen embrittlement during long-term use.
As mentioned above, since the prior methods have problems or disadvantages, an industrially effective method has not necessarily been provided. For example, the known catalyst composed of multiple components still shows an unsatisfactorily low selectivity of the desired cycloolefin, or the known catalysts show only a low catalytic activity, so that cycloolefin cannot be effectively produced. Further, when additives are added to the reaction system, not only does the reaction system becomes complicated but also it is necessary to prevent the deterioration of the reaction vessel. Therefore, there is a demand for a method in which cycloolefin can be produced without addition of the additive the reaction system.
It has been found that the use of a catalyst composed of catalytically active components selected from the group consisting of specific metals and an oxide carrier supporting the catalytically active components is extremely effective for the partial hydrogenation of monocyclic aromatic hydrocarbon.